The M77 is a dual purpose submunition in the category of DPICM (Dual purpose Improved Conventional Munition) dlivered by projectile or rocket warhead and made in the USA. The dual purposes are anti-armour and anti-personnel.

The outer sleeve of the munition is its anti-personnel fragmentation. The interior has a small amount of high explosive above an armour-piercing shaped charge. Despite its short length, the end opposite the ribbon is empty and provides the "standoff" that allows the shaped charge to form and achieve its armour-piercing properties.

The ribbon used is usually white, or green. It unfurls when the submunition is released and orientates the device so that it falls with its shaped charge facing downward. The ribbon loop vibrates as it passes through the air and this vibration arms the device.

When the device lands in an upright position, inertia carries the firing pin into the stab-sensitive detonator and initiates the device.

If the device does not fall for long enough to unscrew the firing pin, it will not be fully armed on arrival.

If there is any obstruction on the thread of the firing pin, the device may not be armed on arrival.

If the device does not land in the correct orientation or strikes obstructions such as buildings or trees, it can fail to initiate. Its ribbon may catch on obstructions and so hold the firing pin away from the detonator.

Moving or handling an unarmed device can rock the ribbon from side to side and allow it to arm.

Moving or handling an armed device can make the firing pin slide forward into the stab-sensitive detonator.

The M77 can kill. If there is any uncertainty about its state, it should always be destroyed where it is.